When plant roots disrupt a septic system, they can cause serious structural damage, unleash foul smells and precipitate health hazards. Turf grasses and shallow-rooted, drought-tolerant ornamental plants are generally safe to plant near septic systems but trees are not recommended. Some trees are particularly forbidden, including willows, poplars and maples.
Some plants have hydrophilic, or water-loving, roots that invade septic systems. Roots penetrate joints in the pipes that feed into septic tanks and cause disruption or failure of the system. Once roots gain entry into pipes, they grow rapidly because of plant nutrients contained in wastewater. Blockages, slow drainage and soggy yards are results of clogged pipes and cracked tanks. Sewage may back up into a house if root obstruction is severe. Repair or replacement costs may be significant, depending on the extent of damage.
Old-time dowsers, or water witchers, chose willow tree (Salix spp.) branches to locate underground springs because of willow’s affinity for water. As dowsers walked around holding forked willow branches in front of them, these divining rods were said to twitch or point downward when they located water; hence, “divining” the location. According to the University of California, willow trees have “adventurous and thirsty roots.” Their adventurous travels lead roots in search of water, which they often find in septic systems. All plants in the Salix genus are capable of aggressive root systems.
Poplars (Populus spp.) with invasive root systems include poplar trees, hybrid poplars and quaking Aspens. In temperate climates, poplars are some of the fastest-growing plants. Their roots must grow aggressively to sustain plants' rapid top growth. Poplars exceed the recommendation of planting hydrophilic plants 50 feet away from septic tanks and drain fields, or leach fields. According to the Association of Bay Area Governments, poplar roots may spread 100 feet from plants to invade sewer lines.
Maples (Acer spp.) should not be planted near septic systems because of their destructive root systems. Silver maple’s roots (A. saccharinum) are so aggressive that they can buckle and lift sidewalks. The University of Florida IFAS Extension cautions that roots from some cultivars can extend from the trunk three times the distance beyond the plant’s drip line. Silver maples are valued for being able to grow in extremely wet soils, but this characteristic is the reason they should not be cultivated near septic systems.
- University of California: Sewer Line Root Control
- SewerSmart.org: ABAG’s Sewer Smart Planting Guide
- University of Florida IFAS Extension: Acer saccharinum "Skinneri" Silver Maple
- Washington State University Extension: Worst Trees to Plant
- University of California RREA Agriculture and Natural Resources: Wastewater
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